Various forms of automatic film processors adapted to develop, fix, wash and dry sheets of exposed photosensitive material are already known to those skilled in the art. In such processors, sheets of material to be processed are fed sequentially from one fluid-containing treatment tank to the next, and the developed, fixed, and washed material is then passed through a dryer and transferred to a collection bin. In the normal operation of machines of this type the chemical solutions employed for processing the photosensitive material tend to become depleted in activity and volume when such material is processed and, unless chemical replenishment is effected during continued operation, severe degradation in the image quality of the developed films will result. It is, accordingly, customary to include some type of controllable replenishment facility intended to maintain the chemical concentrations in the processing tanks at desired and stable levels of activity, and within specific limits of volume and concentration.
Many forms of developer replenishment systems, both manual and automatic, are already known to those skilled in the art, as typified by Van Bouwel, U.S. Pat. No. 3,368,472 which discloses a device for maintaining a developing bath in an automatic film processor at a predetermined level of activity by delivering measured quantities of replenishment fluid to the bath under the control of an electro-mechanical system which detects the arrival of each film sheet and monitors its passage through a physical-contact sensing device located at the input of the processing apparatus. Similarly, Street U.S. Pat. Nos. 3,554,109 and 3,559,555, both assigned to the Assignee of this Application, disclose highly accurate non-contact replenishment control systems which utilize electro-optical scanners to measure and integrate information corresponding to the developed image densities present throughout the complete area of the processed films, and employ this information to automatically control the transfer of precise increments of chemical replenishment fluid from storage receptacles to the processor tanks, in order to counteract the degradation in solution activity which always results from the development of exposed photosensitive material, and which is particularly pronounced in machines utilizing shallow processing tanks having small fluid capacities.
However, despite the high levels of technical sophistication which have been achieved, automatic replenishment systems continue to exhibit sources of inaccuracy, including:
a. A tendency to over-develop images for a short period of time subsequent to each introduction of an increment of replenishing fluid into the main developing tank. This deficiency results from the finite time period which elapses while the replenished developing fluid is returning to the essentially homogeneous state in which it had existed prior to the replenishment cycle.
b. Failure to provide adequate compensation for the gradual loss in developing activity which results from oxidation of the fluid, both during development operations and also while the processor is operative but not engaged in developing film.
When control of replenishment is effected by a film-length or area-sensing measuring system, it is usually very difficult to maintain constancy of developing activity of the developing fluid, because the effective exposed image area of the film to be developed is not known with sufficient precision even though this is the principal source of developer depletion. In other replenishment systems, where the supply of replenishment fluid is controlled cyclically by the detection and integration of increments of information representing the developed image area on the film being processed, it is difficult to obtain consistent replenishment results because the developer activity decreases subsequent to each replenishment cycle and until more replenisher is supplied as a result of the detection and integration of a further predetermined amount of image area information. Furthermore, in conventional prior art film processors, replenishing fluid is usually supplied directly to the developing tank, resulting in an almost instantaneous increase in developer activity, followed soon thereafter by the decrease previously described. Therefore, when continuous lengths -- as opposed to individual cut sheets -- are processed, uneven density of the developed images can easily occur.